Irrigation systems that deliver water, often containing plant nutrients, pesticides and/or medications, to plants via networks of irrigation pipes are very well known. In many such irrigation networks, water from an irrigation pipe is delivered to the plants by “emitters” or “drippers”, hereinafter generically referred to as emitters, which are connected to or installed along the length of the pipe. Each emitter comprises at least one inlet or an array of inlets through which water flowing in the pipe enters the emitter and an outlet through which water that enters the emitter exits the emitter. The emitter diverts a relatively small portion of water flowing in the pipe and discharges the diverted water to irrigate plants in a neighborhood of the location of the emitter.
Generally, to control rate of water discharge by the emitter, the emitter comprises an elastic diaphragm and/or a water flow and pressure reduction channel, a “labyrinth channel” or “labyrinth” through which water that enters the emitter must flow to reach the emitter outlet. The labyrinth channel is a high resistance flow channel along which pressure of water flowing through the emitter drops relatively rapidly with distance along the labyrinth channel. The pressure drop from a relatively high water pressure at the emitter inlet, to a relatively low discharge pressure, generally a gauge pressure equal to about zero, substantially at or near the emitter outlet. The labyrinth channel generally comprises a tortuous “obstacle” flow path that generates turbulence in water flowing in the labyrinth to reduce water pressure and discharge of water by the emitter. Usually, the obstacle path comprises a configuration of baffles that impede and introduce turbulence into water flow.
The elastic diaphragm operates to control liquid flow so that it is substantially independent of inlet pressure for a range of pressures typically encountered in irrigation applications and is equal to a flow rate between about 0.5 and 12 liters per hour (l/h). The diaphragm is usually seated on a support shelf and is located between the inlet and the outlet and constrains water that enters the emitter inlet to pass through the labyrinth to reach the emitter outlet and flow out of the emitter. The diaphragm is responsive to pressure of the entering water, and as pressure of the entering water increases, the diaphragm undergoes increasing distortion. The distortion operates to increase resistance to liquid flow through the dripper with increase in distortion. In some emitters, the distortion increases resistance to water flow through the emitter with increase in inlet pressure by increasing a length of the labyrinth through which liquid is constrained to flow to reach the outlet. Some emitters are formed having an outlet reservoir into which water that flows through the labyrinth empties, and from which water exits the emitter and additionally or alternatively, the increase in resistance may be accomplished by changing a dimension of an outlet reservoir to increase resistance of liquid in the outlet reservoir to exit the reservoir.
An emitter having a flow regulated so that it is substantially independent of inlet liquid pressure is referred to as a regulated emitter.
Labyrinths and various other liquid flow channels in emitters have a tendency to become blocked by particulate matter, such as dirt, debris or agglomerations of plant nutrients that may be carried by liquid that flows through the emitter during plant irrigation from irrigation pipes in which the emitters are mounted. In addition, emitter outlets and flow channels have a tendency to get clogged with dirt and debris that are sucked back into the emitters by water and/or air backflow. Water and/or air backflow typically occurs when supply of water to irrigation pipes providing water to plants in a field or hothouse is turned off and pressure in the pipes falls. For subsurface drip irrigation (SDI) pipes, which are buried in the ground or a growing medium, particulate matter in the surrounding soil or growing medium tends to be drawn into and clog emitters in the pipes when water pressure in the pipes falls. For above surface drip irrigation, backflow tends to clog emitters by drawing into the emitters particulate matter in mud and dust in environments in which the emitters often are located.
To reduce a probability of particulate matter carried by liquid flowing in irrigation pipes from entering and clogging emitters mounted in the pipes, emitters are generally designed having various types of inlet filtering configurations. The inlet filters tend to prevent particulate matter greater than a given size that may be carried by irrigation liquids in the pipes from entering the emitters. Internal liquid flow channels of the emitters are formed sufficiently large so that particulate characterized by a size less than the given size that are passed by the filters do not clog the channels. To reduce a probability that dirt and debris is sucked back into emitters when water pressure is reduced in the pipes emitters have been designed to seal themselves against back flow when pressure in an irrigation pipe in which they are installed is reduced. Such drippers, commonly referred to as “anti-siphon” or “non-return” emitters, are usually configured having an elastic diaphragm that sets on and seals an inlet orifice of the emitter.
U.S. Pat. No. 6,027,048, the disclosure of which is incorporated herein by reference, describes a regulated non-return agricultural emitter comprising a filter configuration, a labyrinth, and an elastic diaphragm that seals the emitter against “backflow”. The inlet configuration comprises two relatively long inlet channels that “are relatively larger in width than those of conventional emitter units”. Each inlet channel has an array of “filter baffles” along its length and is “undercut” in an outside surface of the emitter so that it is partially covered with a lip that runs along the length of the channel. The baffles and lip operate to prevent particulate matter in liquid carried by an irrigation pipe in which the emitter is installed and that might clog the emitter from entering the inlet channel. The two inlet channels communicate via a coupling channel to a “single restricted inlet” through which liquid from the irrigation pipe in the inlet channels enters the emitter. An elastic diaphragm operates to regulate liquid flow through the emitter. To provide a non-return function, the diaphragm seals the single restricted inlet when water pressure in the irrigation pipe is reduced below a desired threshold pressure.
The patent notes that the use of “inflow paths which are relatively larger in width than those of conventional emitter units” aids in “minimizing the dangers of blockage”, and are “of particular significance where, as in the emitter unit specifically described and illustrated, a non-return valve construction is provided for. With such a construction, only a single restricted inlet . . . into the emitter unit is available, and such a restricted inlet could not accommodate adequate filtering means.”
U.S. Pat. No. 5,615,838, the disclosure of which is incorporated herein by reference, describes integrated emitters, referred to as in-line emitters, that have a non-return feature and optionally provides a regulated flow of water. In an embodiment of the invention, a flexible membrane closes the emitter to flow into or out of the emitter when inlet pressure to the emitter falls below a minimum pressure. The membrane optionally functions to control a length of a labyrinth through which water flows responsive to inlet pressure to regulate flow of water provided by the emitter.